Colin Powell only endorsed Barack Obama because he is black, says Mitt Romney's aide

A senior aide to Mitt Romney has played the race card for the first time in the presidential campaign as new polling reveals that it is the most racially polarised election in more than two decades.

John Sununu, a former White House chief of staff, suggested in a CNN interview on Thursday that the former secretary of state Colin Powell, a respected member of the Republican establishment, had endorsed President Barack Obama because he was a fellow African American.

Mr Powell, who broke with his party to vote for Mr Obama over the Republican candidate, John McCain, in 2008, ignited a new firestorm among Republicans for endorsing Mr Obama and criticising Mr Romney for his foreign policy flip-flops.

Asked by the interviewer Piers Morgan about the Powell endorsement, Mr Sununu said: "When you take a look at Colin Powell, you have to look at whether that's an endorsement based on issues or he's got a slightly different reason for endorsing President Obama. I think when you have somebody of your own race that you're proud of being President of the United States, I applaud Colin for standing with him."

Mr Sununu has put into the public domain the issue that Mr Obama has only rarely mentioned during the first term of his presidency. But many in Washington have long suspected that the Republican Party's relentless opposition to Mr Obama and its members' denigration of his presidency stem from the fact that he is black.

Mr Sununu has a history of making thinly veiled racial comments about Mr Obama, describing him as "lazy" and accusing him of instituting "class warfare". He has also suggested the president is un-American because he was brought up in Indonesia.

Polling evidence presented in a new Washington Post/ABC News survey says this is the most racially charged presidential election since 1988 when George Bush and Michael Dukakis went head to head.

Mr Obama is trailing Mr Romney in support from white voters by 60 per cent to 37 per cent. His deficit is particularly marked among white male voters, although he remains ahead of Mr Romney with women voters. According to Thursday's poll, almost all black voters say they intend to vote for Mr Obama on 6 November, as will 80 per cent of Hispanic voters. Meanwhile 91 per cent of Mr Romney's support comes from white voters.